Rotary pumps

ABSTRACT

A pump of the eccentric rotor offset sliding blade type has the blade slots of such depth, in relation to the length of blades approaching the fully worn condition, that upon re-starting after stoppage worn blades remain retracted in their slots and cannot escape to cause jamming and damage to the pump.

United States Patent n 1 n 1 1, 82

Home I Feb. 12, 1974 [54] ROTARY PUMPS [56] References Cited [75] Inventor: Robert Hor'ne, Cheltenham, UNITED STATES PATENTS England 2,674,953 4/1954 Conde 418/236 [73] Assignee: Lacy-Hulbert and Company Limited, Beddington, Croydon, Primary Examiner-C. J. Husar Surrey, England Assistant ExaminerLeonard Smith Attorney, Agent, or FirmDwight Hunter Smiley; [mi- [22] FllLd. Nov. 22, 1972 rie and Smiley [21] Appl. No.: 308,821

[57] ABSTRACT [30] Foreign Application Priority Data A pump of the eccentric rotor offset sliding blade type Dec. 20, 1971 Great Britain 58,992/71 ha th blad slots of such depth, in relation to the I length of blades approaching the fully worn condition, UeS- Cle that upon re.. ta -ting after stoppage worn blades rc Int. main retracted in their lots and -cannot esca e to [58] Field Of Search 418/115, 151, 234, 236, 237, ause jamming and damage to the pump.

1 Claim, 1 Drawing Figure ROTARY PUMPS This invention concerns improvements in rotary pumps of the eccentric rotor, sliding blade type. One kind of pump of this type has the blade slots tangential to a circle concentric with the rotor axisythis kind of pump is known as the offset blade type.

Offset blade pumps are very reliable in use, but, in

common with other types of sliding blade pumps, they are liable to serious damage and jamming if a blade escapes from its slot when it is foreshortened beyond a certain degree by wear at the tip.

It is an object of the invention to obviate the possibility of blade escape despite maximum allowable or exce'ssive blade tip wear in'intermittently operated pumps of this kind.

According to the invention we provide an intermittently operated eccentric rotor offset sliding blade type pump having blade slots whose depth is chosen in relation to fully worn blade length such that the centre of gravity of a fully retracted worn blade lies behind the radius of the rotor intersecting its guide slot at right angles.

The expression-behind used in the above definition signifies displaced angularly contrary to the direction of pump rotation, as will be-understood by those versed in the art.

Blades become fully retracted in their slots when the pump rotor is slowed down and stopped and are thrown out by centrifugal force to contact the inner surface of the stator upon re-starting, so long as their centres of gravity lie ahead of the aforementioned radii. However,

if their centres of gravity lie behind these radii, i.e. towards the slot bases, contrifugal force tends to keep them retracted.

Blade slots of pumps in accordance with the invention are abnormally deep, and experience shows that no more than three can be provided in a small rotor without fear of introducing weakness where the base of one slot approaches the side of an adjacent slot. However, in large pumps it will almost certainly be found possible to accommodate several additional slots.

in the ordinary course of events, it is ensured by pump designers that blade retraction will not be maintained, so that a pump will operate effectively throughout the period of blade life. In contra-distinction a pump according to the present invention will fail safe. That is to say, pump efficiency will be so obviously dimished that the requirement for blade replacement will be made evident before a damaging situation can arise.

The principle of the invention is illustrated in the accompanying diagrammatic drawing, which shows a rotor A driven by a shaft C in a stator casing B.

A fully worn blade D is shown in its extended position in contact with the stator wall. About half its length extends out of its guide slots and it can operate safely in this condition. The blade, referenced D1, is also shown in its fully retracted position, which it assumes when the rotor is stopped, and it can be seen that its centre of gravity X lies behind the radius R from-the rotor axis which intersects the guide slots at right angles.

When the rotor is started, the blade will remain in the retracted position and loss of efficiency will indicate the necessity for blade replacement.

The principle of the invention is certainly applicable j sliding blade pump wherein guide slots for the blades are of such depth that the centre of gravity of a fully retracted blade when worn to the maximum allowable extent lies behind the radius of the rotor which intersects its guide slot at right angles. 

1. An intermittently operated eccentric rotor offset sliding blade pump wherein guide slots for the blades are of such depth that the centre of gravity of a fully retracted blade when worn to the maximum allowable extent lies behind the radius of the rotor which intersects its guide slot at right angles. 